JP 2013-107624A (Reference 1, FIGS. 36 to 38) discloses a known seat driving apparatus in the related art, for example. The apparatus includes a worm wheel that is an input shaft rotationally driven by the rotary motor, and for example, a tubular member into which a lifter shaft that is an output shaft linked to a lifter mechanism is fitted so as to integrally rotate therewith and to be relatively movable in an axial line direction. The tubular member includes a tubular portion and a flange-like pressing piece which protrudes outwardly from the tubular portion. The tubular member is fitted so as to cause the worm wheel to be integrally rotated in response to movement in the axial line direction toward the worm wheel. The tubular member is biased in the axial line direction toward the worm wheel by a compression spring interposed between the tubular member and the lifter shaft.
The seat driving apparatus includes an intermediary member into which the tubular portion is loosely inserted and which is turnable about an axial line extending in a direction different from a direction of an axial line of the tubular member, and a cam member which is turnable about an axial line extending in a direction different from the directions of the axial line of the tubular member and the axial line of the intermediary member. The cam member presses the pressing piece via a distal end portion of the intermediary member so as to release the fitted worm wheel from the tubular member against biasing force of the compression spring by pressing the distal end portion of the intermediary member when being at a neutral position. The cam member allows the worm wheel to fit into the tubular member biased by the compression spring in response to turning force from the neutral position. The cam member is biased so as to be held at the neutral position.
Incidentally, according to Reference 1, for example, there is a case where the tubular member and the worm wheel mesh with each other when being integrally rotated. Such meshing becomes evident in the upper limit and the lower limit within a range of positional adjustment, for example, by being applied with an excessive load when the turning of the lifter shaft is locked. At this time, there is a possibility that the fitted worm wheel is unlikely to be released from the tubular member. Meanwhile, it may be considered to cope therewith by increasing the biasing force for holding (restoring) the cam member at the neutral position. However, in this case, another disadvantage is caused in that operation force for turning the cam member from the neutral position increases.